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Acid/alkali color changing demo for Cub Scouts

Q. I am a Scout leader who wants to do a color changing demo as part of one of our advancement ceremonies. This is what I want to show:

Clear liquid to orange (can be reddish orange) liquid to yellow liquid to blue liquid

I was thinking that starting with an acid with a pH of 2.8 or so would give the clear liquid to orange by adding thymol blue. Increasing the pH would change the color to yellow. Continuing to increase the pH to 8.0 should change it to blue.

My question is, what are some reasonably safe, obtainable acids and bases to make this happen? I am envisioning adding the indicator to beaker 1 for orange. Adding the contents of beaker 2 to beaker 1 for yellow; then adding the contents of beaker 3 to beaker 1 for blue.

This symbolized the Scout before attaining rank; attaining the rank of Tiger; attaining the rank of Wolf; and finally attaining the rank of Bear.

Any help would be most appreciated!

Sandra House
- Phoenix, Arizona USA
February 16, 2017

Q. Thanks. I am looking at thymol blue for the indicator because it has the right colors as the solution goes from acid to neutral to base. Sandra House [returning] - Phoenix, Arizona USA February 16, 2017 A. Aqua Ammonia (ammonia gas dissolved in water) -- sometimes called ammonium hydroxide -- is a good choice for this sort of experimentation. It's cheap at your local supermarket (get the clear, not the soapy). And (neat trick for Cub Scouts) if you hold damp litmus or pH paper above it you can see the color change from neutral to alkaline with the volatile ammonia absorbed by the water in the indicator paper. I still remember (60+ years ago) my Dad mixing vinegar and aqua ammonia ⇦this on eBay or Amazon [affil links] to show me that heat was generated when acids and alkalies mix. Tom Rochester CTO - Jackson, Michigan, USA Plating Systems & Technologies, Inc. February 21, 2017